Snap action electrical switch



Jan. 3, 1956 F. J. BROCH 2,729,715

SNAP ACTION ELECTRICAL SWITCH Filed Aug. 25, 1952 5 Sheets-Sheet 1 Jan. 3, 1956 F. J. BROCH SNAP ACTION ELECTRICAL SWITCH Filed Aug. 25, 1952 5 Sheets-Sheet 2 Jan. 3, 1956 F. J. BROCH 2,729,715

SNAP ACTION ELECTRICAL SWITCH Filed Aug. 25, 1952 5 Sheets-Sheet 3 .,lia/jenlar f? 'aderz'ah/j )5; 00A,

Jan. 3, 1956 BROCH 2,729,715

SNAP ACTION ELECTRICAL SWITCH Filed Aug. 25, 1952 E SheetS-Sheet 4 J V I w TM k K {71/ j. Z 35 P fly fy 14 4 [V 64 P! if 35;

F. J. BROCH SNAP ACTION ELECTRICAL SWITCH 5 Sheets-Sheet 5 Jan. 3, 1956 Filed Aug. 23, 1952 United States SNAP ACTION ELECTRICAL SWITCH Frederick John Broch, Cambridge, Mass. Application August 23, 1952, Serial No. 306,049 13 Claims. (Cl. 200-67) This invention pertains to electrical switches of the general type customarily known as snap action switches, examples of which are disclosed in the patents to Leupold, No. 1,780,758, November 4, 1930, and McGall, No. 1,960,020, May 22, 1934, such switches being widely used in the arts and industries, especially where a substantial current must be controlled by a switch of small dimensions and often in response to a very small amount of motion of the actuating element, for instance, the maximum motion of the actuating element available to throw the switch may be of the order of a few tenths of a thousandth of an inch. Moreover, the force available for operating the actuator is in many cases very small,

for instance, a force such as results from the operation" of a sensitive, temperature-responsive, bimetallic element or from the motion of an aneroid diaphragm or the like. Such switches are often located in places where they are subjected to severe shocks or to constant vibration, for example, in aeronautical installations. Obviously a switch so employed must be highly resistant to shock and vibration to avoid accidental closure or opening of the controlled circuit, and to be of commercial value must be capable of embodiment in a structure of those standard outside dimensions which have come to be recognized in the art.

Moreover, when snap action switches of certain types are used in places where they are subjected to constant vibration, it has been found that the contacts burn out very quickly because, at the instant at which the contact pressure is released, the external vibration produces a multitude of makes and breaks before the contacts are separated far enough to prevent arcing. For this reason it has been found necessary heretofore, in many installations, to sacrifice sensitivity in the interest of providing a normal contact pressure great enough to prevent such vibrational motion or bouncing of the contacts.

Switches of this type are more usually so devised that motion of a single actuator element in one direction will, for example, close the switch, while release of the actuator will allow the switch automatically to open.

In my copending application Serial No. 191,447, filed October 21, 1950, I have described a novel snap switch and have described and illustrated its principle of oper-.

ation, as embodied in a double-snap action switch, by geometric diagrams as well as in practical embodiments. The present invention employs certain of the basic features described in said copending application but combines therewith certain novel structural relations whereby the sensitiveness of a snap action switch, whether single or double action, may be greatly increased. This" novel structural arrangement, herein for the first time disclosed, involves the used of a fulcrum or deflector for the spring-stressing, spring-supporting or tensioning element of the switch so devised that the fulcrum point or place of flexure of said tensioning element is spaced from that part of the tensioning element which is fixedly anchored to the base and is located at one end ofan elongate rigid portion of the tensioning element to which rigid portion the actuating force is preferably applied. In its preferred embodiment the fulcrum has a convex arcuate contact surface on which said end of the rigid portion of the tension element rests and over which the tension member of the switch is stressed, much as a violin string is stretched over the bridge, with the fixed anchorage for the tensioning element arranged closely adjacent to and at that side of the fulcrum which is away from the switch contacts.

Since the primary function of the spring stressing element, spring suppo spring resistor or spring tensioning element is to hold the switch spring under restraint, the tensioning member need not and desirably should not be resilient although, as a practical matter, any material, which is at present known to me, and having the requisite tensile strength and other requisite characteristics, will have a certain amount of transverse resiliency. As herein illustrated, by way of example, the spring is a compression spring, but when the term spring tensioning element is sometimes here employed that term is not to be understood as implying that the springv is necessarily elongated or stretched, but only that it is stressed.

In theory, at least, for optimum effect, this tensioning member should have hinge joints at at least two points in its length, and in addition should have a hinge connection to the compression spring. In accordance with the present invention, the latter hinge is actually provided,but because of limitations of space and cost, among other things, the provision of hinges at the other points is impractical and thus a tensioning element of freely bendable, flexible material is employed. By the term freely bendable it is intended to suggest that the part ofiers little effective resistance to bending, so that at the place of flexure it behaves nearly as though it were actually hinged at that point. When herein reference is made to a hinge or hinge connection, these terms are to be understood as inclusive of actual pintle-type joints as well as a capability of flexing of thin sheet material to form a definite angle comparable to that resultant from'the relative rocking of rigid parts about an actual joint. A metal of high tensile strength but of slight thickness,'for example, beryllium bronze of the order of 0.006 inch thick, has been found to provide a reasonably good solution to the problem for while it is not actually limp it does provide, the desired flexibility and resistance to elongation being without undue resilient opposition to transverse bending.

On the other hand, the spring member must be sufficiently resilient to insure a quick snap action. Beryllium copper alloy of the order of 0.007 inch thick is useful. Certain features of the present invention, as hereafter pointed out, are equally applicable to a singleaction switch or to the double-action switch described in the aforesaid application.

Among the principal objects of the present invention are to provide a snap switch of such a design that max imum pressure between the contacts subsists at the very instant of separation, thereby assuring long life of the contacts and the maintenance of the initial characteristics of the switch throughout a long life of service, while at the same time providing a switch having a high degree of sensitivity.

Other objects of the present invention are to provide a snap action switch which is highly resistant to shock and vibration; to provide a switch which is of longer life than most switches of this type; to provide a switch of a, design which minimizes lost motion between the parts, a highly desirable feature in view of the very slight magnitude of the motions involved, thereby providing a high degree of sensitivity and accuracy; to provide a switch which may readily be constructed to respond to a very small actuating force or to the movement of an actuator which moves a very, short distance; to provide a switch which is readily and sensitively adjustable to respond to actuating forces of different amounts; to provide a switch having the above characteristics which may be, of those outside dimensions which have come to be accepted as standard in the industry, and which is simple in construction, whether it be a single-action switcher a double-action switch; to provide a switch having the above characteristics but which is durable and'inexpensive to manufacture; and to provide a snap action switch which, in general, is superior in construction and function to switches at present available on the market. Other and further objects, and advantages of the invention will be pointed out in the following more detailed description and by reference to the accompanying drawings. in which- Fig. 1 is a plan view of a simple, single-action snap switch according to the present invention, the cover of the switch case being removed;

Fig. 2 is a longitudinal section substantially on the line 2.2,of, Fig. 1';

Fig. 3 is a side elevation of the base of the switch shown in Fig. 1;

Fig. 4 is a plan view of the base shown in Fig. 3;

Fig. 5 is a perspective view of the tension member;

Fig. 6 is a perspective view of the compression spring before it is bent to its arcuate, operative shape;

Fig. 7 is a perspective view of the normally stationary abutment for the fulcrum end of the compression spring;

Fig. Sis a perspective view of a desirable formof actu ator;

Fig. 9 is a fragmentary, transverse section, to larger scale, on the line 99 of Fig. 2; V

Fig. 10 is a fragmentary, horizontal section, to larger scale, through the cover of the switch illustrating one desirable arrangement for guiding the actuator of Fig. 8;

Fig. 11 is a plan view of a double-action switch embodying the present invention, the top or cover of the switch being removed;

Fig. 12 is a side elevation of the switch of Fig. 11, with the cover in place but in a section substantially on the line 1212 of Fig. 1-1;

Fig. 13 is a perspective view of the combined spring abutment. and contact-carrying arm; i

Fig. 14 is a plan view of the spring employed in the double-action switch before it has been bent to operative shape; i

Fig. 15 is a diagram illustrative of a principle of operation employed in the switch disclosed in my aforesaid copending application;

Figs. 16, 17 and 18 are diagrammatic views illustrating the principle of operation of a single-action snap switch andof the primary action movement of a double-action switch of the present invention;

Fig. 19 is a plan view of the switch of Fig. 1, but to smaller scale, with the cover removed but showing a slight modification of the carrier for the upper electrical con: tact;

Fig. 20 is a fragmentary, vertical section illustrating a modified arrangement for adjusting the normal position of the upper contact;

'Figs. 21 and 22 are diagramsillustrative of-the princi: ple of operation of the double-action switch shown in Fig. 12;

Fig. 23 is a fragmentary side elevation of a modification;

Fig. 24 is a fragmentary side elevation of a further modification;

Fig. 25 is a fragmentary, plan view of the cover of the switch, illustrating a modified form of actuator button;

Fig. 26 is a fragmentary, longitudinal, verticalsection through the cover and base of the switch illustratinga,

modified form of actuator and tensioningelement; and

Fig. 27 is a fragmentary, transverse section, showing the same parts as Fig. 26.

Referring to the drawings, and particularly to the illustrative embodiment of Figs. 3 and 4, the base 20 of the switch consists of a generally rectangular, substantially rigid block of an appropriate mouldable, preferably dielectric, material, for example Bakelite, hard rubber or the like, its external dimensions preferably being those which have become substantially standard for snap switches of this general type, for instance of a length of 1 a width of 1 and a depth of with the axis of the actuating pin at a distance of approximately /2 from one end. The base here illustrated is designed for alternative use in a single-action switch or in a double action switch respectively. Preferably this base has a fiat marginal upper surface 21 for contact by the lower edge of the removable cover 22 (Fig. 2).

At its right-hand end, as viewed in Figs. 3 and 4, the base has a substantially flat upper face 23 elevated above its marginal edge 21. As here illustrated, by way of example," an internally screw threaded metallic bushing 24 (Fig. 3) is fixed in the base block with its axis perpendicular to the face 23 and located approximately symmetrically'with respect to the lateral faces of the base, the upper endof this bushing projecting above the surface 23' and having a flat top surface 25. The bushing 24 is designed to receive a terminal post (not shown) to which oneof the conducting wires is attached. Adjacent to one side of the base at its left-hand end is an internal- 1y screw threaded metallic bushing 26, fixed in the sub stance of-the block, the upper part 27 of this bushing projecting to a substantial distance above the upper we face of the block and being diametrically split at 23 so that it'may resiliently grip the screw threaded shaul-z (Fig. 2) 'of a'vertically adjustable electrical contact screw 30 (Fig. 2).' Adjacent to the opposite side of the base block an internally screw threaded metallic sleeve (Figf 4)"'is fixed in the substance of the block with its axis perpendicular to the under surface of the block, this sleeve projecting up to a height greater than the sleeve26 and having a fiat, upper surface 32 (Fi 3) which forms a support against which a bracket arm 33 (Fig. 11) may be clamped by means of a screw 34. Preferably this bracket is so constructed as to provide a horizontal slot (Fig. 9) for the reception of a portion of a contact carrier 87 (Fig.2) which extends transversely of the base so as to overhang the contact 3 the carrier 87 supporting an upper contact disk which is vertically spaced from contact 30. in the single action switch, the bracket 33 is not employed (see Fig. l) and in that event the contact carrie'r 87 may be clamped directly to the surface 32 by the screw 34. If desired, the metallic bushings or sleeves may be omitted, the terminal posts being moulded into or otherwise fixed in the material of the, base, and the screws, here shown as entering the upper ends of'the bushings, being threaded directly into bores" in the material of the base itself.

Preferably, thelcontact carrier 87 (Figs. 1, 2 and 11.) is ofresilient material and is normally biased to urge the u per contact upwardly away from the contact 30. The normal position'of the upper contact may then be adjusted by ascrew 290 having threaded engagement with the walls of a bore (Fig. 9)'in the cover 22, the screw having af headf 291 by 'means of which it may be turned. turning the screw the contact carrier 87 may be flexed downwardly, thus moving the upper contact toward the contact '30. This arrangement permits the user of the switch tola djust the normal position of the upper contact. However, it may be preferred that this adjustment be a permanent adjustment made during manufacture of the switch, "an with this. in view the arrangement of Fig. 20 may beemployed. In this arrangernent a short screw 29?. engages a threaded bore in the cover, the screw being provided with aslot in itsupper end. The screw is turned it i m nur to adjustthe upper contact to the most advantageous position and then a cover disk 293 is placed over the upper end of the screw and permanently secured by adhesive, or otherwise, to the cover 22 so that the screw is no longer accessible.

When the base is used in a double action switch, the bracket 33, as shown in Figs. 11 and 12, supports the vertically adjustable stop screw 35.

The base block has ribs 36 and 37 (Fig. 4) at its opposite sides adjacent to the marginal surface 21 and projecting above the latter. At their widest, the right-hand portions of these ribs (as here illustrated, Fig. 4) are desirably of a width of the order of one-eighth of the width of the base proper, the ribs being spaced in from the side surfacesof the base a distance substantially equal to the thickness of the wall of the cover 22. The right-hand portions 38 and 39 of the ribs 36 and 37, as viewed in Figs. 3 and 4, are higher than their left-hand portions, gradually increasing in height toward the right-hand end of the base and then declining abruptly (Fig. 3), and having curved upper surfaces 40 and 41 near their right-hand ends the ribs terminating a short distance away from and to the left of the surface 25. These upwardly convex portions of the ribs are hereinafter referred to as deflectors, as humps or as fulcrum members.

The highest points of these humps are above the level of the surface 25. Midway between ribs 36 and 37 the base block may have a transverse depression 42 (Figs. 2 and 4) in its upper surface. At opposite sides the block may have recesses 43 in its outer faces to receive retaining ears (not shown) formed on the cover. The upper surface of the base is also provided with a shallow dimple 44 midway between the ribs 36 and 37.

In a switch of the single-action type, a normally fixed spring abutment 45 (Figs. 2 and 7) is mounted on the base between ribs 36 and 37. This abutment 45 is here illustrated as a piece of material of elongate, generally rectangular contour which, though normally immovable and functionally substantially rigid, is capable of being bent slightly for adjustment. Its left-hand edge is provided with a transverse V-notch 49 (Fig. 7) for the reception of the rear edge of the compression spring. The end portion 4'7 is furnished with a screw threaded hole 50 for the reception of an adjusting screw, hereafter described. Preferably, to avoid the necessity for a lock nut for this adjusting screw, the part 47 has a slot 51 extending from its free edge to the hole 50, the parts at opposite sides of the slot being bent toward each other so that when the screw is inserted in the hole 50 it is resiliently gripped and thus held in adjusted position. The end portion 48 of the spring abutment has a hole 52 which, when the 1 parts are assembled, is coaxial with the bushing 24.

The spring tensioning element 53 (Fig. 5) consists of very flexible sheet material, for example copper-beryllium alloy, of the order of 0.006 inch in thickness, having little effective resiliency to resist transverse bending, and which has substantial tensile strength and although capable of taking a permanent set when bent sharply is substantially non-stretchable in response to the forces to which it is subjected in the switch structure. This spring tensioning element may be made by die-cutting a blank from the selected sheet material and then bending it to final shape. As illustrated, by way of example (Fig. 5), this tensioning element comprises the transversely spaced, elongate, parallel arms 54 and 55 which are integrally joined at their left-hand ends by a transverse web 56, the latter having a relatively narrow end portion 57 whose free margin is sharply bent downwardly to form the transversely elongate hook 58. The inner edges of the arms 54 and 55 are spaced apart a distance such as to receive between them, with clearance, the spring abutment 45, the tension element thus having the form of an open frame with a large substantially rectangular central aperture.

At the right-hand end of the tension element its arms 54 and 55 are integrally joined by a transverse web 59 whose free right-hand margin is sharply bent at 60 to form a stiffening rib and which has an anchoring tab 61 projecting inwardly from its left-hand margin. This tab has a hole 62 for the reception of an anchoring screw and, at opposite sides of the tab, the web 59 is shaped to provide aligned fulcrum edges 63 and 64 which are of utility in the double-snap switch, as hereinafter described, although having no function in the single-snap switch. It will be noted that the center of the hole 62 is to the left (Fig. 5) of the points at which the arms 54 and 55 join the web 59, thus providing for a greater effective length of the tensioning element than though the hole were within the width of the web proper. By providing a tension element of as great an effective length as is possible within the permissive confines of the switch structure, sharp bending of the tensioning element is avoided. Between the points 65 and 66 of the arm 54 and between the points 67 and 68 of the arm 55 the marginal portions of the respective arms are sharply bent down to provide integral stiffening flanges 69 and 70. As illustrated by way of example, these flanges turn downwardly, at right angles to the respective arms, but they may be turned upwardly if preferred. These flanges are of such vertical depth as to make those portions of the arms 54 and 55, from which the flanges project, substantially rigid, these rigid portions of the arms acting as levers in the operation of the switch, as hereafter described. While these stiffeningflanges constitute simple and effective means for making these portions of the arms rigid, it is contemplated that other and equivalent means for stiffening the arms may be substituted. Imaginary lines extending transversely across the tension element, at the opposite ends of these stiffened portions, locate two of the lines of fiexure or hinge axes of the tension element.

The compression spring 71 (Fig. 6) for the single action switch may be made from any suitable spring material, for example, beryllium-copper or bronze and may, for example, be of a thickness of the order of 0.007 inch, being die-cut from the sheet stock and then bent to the desired shape. As illustrated in Fig. 6, by way of example, the spring comprises the elongate, substantially rectangular portion 72 (which constitutes the spring proper) having a substantially straight edge 73 at its righthand end. At its left-hand end the part 72 merges with a head portion 74 transversely wider than the part 72, this head 74 being bent transversely at 75 so as to provide the upstanding flange 76. The included angle between the part 74 and the flange '76 is preferably approximately In the angle where the parts 74 and 76 join, an elongate slot 77 is provided, this slot being vertically widened at its opposite ends as indicated at 78 and 79, providing between these widened portions a transversely elongate fulcrum edge 80. The flange 76 has an integral bracket portion 81, in a plane substantially perpendicular to the plane of the flange proper, this bracket being of a width approximately one-half that of the flange and being unsymmetrically located, that is to say it is nearer to one side of the spring member than to the other side. As herein illustrated (Fig. 2), the abutment 45 is located nearer to the left hand end of the base than to the right hand end, and the bracket 81 is very close to the left hand end of the base. By placing the fixed contacts at one side of the longitudinal center line of the base, and by mounting the movable contact button on the off-center bracket 81, it is possible to locate the abutment 45 nearer the left hand end of the base than has previously been the practice and thus to lengthen the tension element 53, beyond any length heretofore possible in a switch of standard dimensions.

In accordance with one desirable procedure in assembling the parts such as above described, in making the single-action switch of Fig. 2, the web portion 59 of the spring tensioning element 53 is disposed upon the surface 25 of the base, with the hole 62 in the tab 61 coaxial with the bushing 24. The abutment member 45 (Fig. 7) is then 7 arranged so that its end portion 48 rests. upon the tab 61 of the spring tensioning element, and an anchoring screw 83 (Fig. 12 is passed down through the holes 52 and 62 and screwed into the bushing (or into the base if no bushing is used) until the head 34 of the screw contacts the upper surface of the part 48,, thus clamping the parts 45 and 53 firmly to the base and providing a fixed, secure and firm anchorage for the right-hand end of the tensioning element 53. Since the surface 25, on which the tab 61 of the tensioning element rests, is in a plane higher than that of the upper surface of the central portion of the base, the abutment & acts as a stiffiy flexible beam supported at one end but which is capable of being flexed so that its left-hand free edge moves up or down. As here illustrated by way of example, the abutment is so normally biased that its free end, unless forcibly held up, would be at the lowest position which it shouldv ever occupy. Toprovide for adjustment of the free end of the abutment, a screw 85 (Fig. 2) is threaded into thehole 59 of the abutment 45 so that its lower end seats in the dimple 44 in the base block. he screw has a slotted head 86. by means of which it may be turned, the advance of the screw lifting the end 47 of the abutment member while reversal of the screw permits the end of the abutment member to descend. A

screw for holding the cover in place might also be arranged to perform the above-described function of the screw 86.

According to one possible procedure in assembling the parts, the hook portion 58 of the spring tensioning element 53 is passed through the slots. '77 in the spring 71 and engaged with the fulcrum edge thus providing a hinge connection between the parts. The part 72 of the spring is then flexed or bowed downwardly, as shown in Fig. 2, until its edge 73 may be snapped into the V-slot- 49 of the abutment 45. When the parts are thus assembled, the spring tensioning member 53 is held under longitudinal tension by the spring 71 and conversely the compression spring 71 is maintained in its downwardly bowed form by the tensioning element. Since the surface 25 on which the tab 61 of the spring tensioning elements 53 rests is in a plane below the level of the uppermost points of the humps and 41, the tensioning element is bowed upwardly over these humps and held taut in contact with the upper curved surfaces of the humps in a manner similar to that in which a violin string is held taut over the bridge.

An actuating pin 88 is movable up and down, with clearance, in a bore in the cover 22. The lower end of this pin is fixedly connected, preferably integrally, with a transverse yoke 39 (Figs. 8 and 10), having at its opposite edges pressure-applying lugs 99 and 1 (Fig. 8), preferably having arcuate lower ends, which rest upon the upper surfaces of the stiffened or lever portions of the legs 54 and 55 respectively, of the spring-tensioning element. Toprevent orientation of the yoke 89, which might disengage its lugs from the legs 54 and 55, the pin may be provided with vertical ribs or laterally projectingpins 92 (Fig. 10) at itsopposite edges which slide freelyin vertical grooves 93-formed in the inner surfacesof the side walls of the cover 22. Alternatively, the pin may be of polygonal transverse section, as shown at 83 (Figs. 25 to 27) arranged to fit loosely in a hole of corresponding contour in the cover.

The points of contact of the lugs ht) and 91 of the actuator, with the stiff portions of the legs and of the tensioning element are located to the left of the points of tangency of the legs 54 and 55 with thecurvcd surfaces of-the humps 40 and (such points or lines of tangency, as above suggested, define the fulcrum or hingeaxisof the rigid portions of legs 54 and 55). Thus when the actuator is depr essed, the applied force tends to rock the stifiened rigid portions of the legs 54. and 55 in a counterclockwise direction about said points of tangency as a fulcrum line, The stiffened portions of. the arms thus act as levers of-the second; order, and (according to the distanee, betvveer the neof action .of .the actuating force and the fulcrum points 1 may providev for substantial multiplication of the effective motion of the actuator.

In arrangements such as that illustrated, for example in the switch of Fig. l, where the contacts are located unsymmetrically, there is a tendency for the spring tensioning element to Warp slightly because of the normal pressure of the movable contact against the upper fixed contact. Thus one arm of the tension element may normally be higher than the other and when actuating force is applied, some of the force would be wasted in first returning the tension arms to the same plane. I t is contemplated that the spring-contacting elements of the actuator, for example, the parts and 91 of Fig. 8, may be arranged so that the eifective pressure applied to the respective arms 54 and 55 is slightly different, as for example, by making the parts 90 and 91 of sli htly different depths, vertically, so that a slightly greater amount of force will be applied to one of the legs of the tensioning element than to the other, or by any equivalent arrangement compensating for the tendency to warp.

One form of double-acting switch embodying the principle of the present invention is illustrated by way of example in Figs. 11 to 14 inclusive. This double acting switch employs the same base 2i) as the single-action switch above described, and the same cover, the same spring tensioning element and, if desired, the same actuator 88. However, in place of the spring '71 of Fig. 6, with its attached contact-supporting bracket 81, a simpler spring 71 (Fig. 14) may be used. Spring 71 comprises a rectangular portion 72 which constitutes the spring proper, having the rectilinear right-hand edge 73 and being integrally joined at its lcft-hand end to the transversely wider head portion 74*, the latter having a rectilinear fulcrum edge 869 extending between spacedpositioning ears and 16 In place of the spring abutment 4-5 of the singleaction switch, a combined abutment and contact carrier 102, such as illustrated, by way of example, in Fig. 13 is used. This part 102 is a rigid member, desirably formed from sheet material and comprises a bifurcated righthand end portion 103 having a transverse V-notch we in its edge and having a recess, centrally located, which extends inwardly from said edge for the accommodation of the upper end of bushing 2- assuming that the latter is used. The abutment member 102 comprises the body portion 186, from the left-hand end of which a flange 107 projects upwardly, substantially at right angles to the part 106, and from the upper edge of this flange an arm 108 extends first downwardly and then horizontally or slightlyupward to form a support for a contact button 109. At the junction of the parts The and iii? an external, transversely extending \/-notch 11% is provided. As shown in Fig. 11, this part 1 8? is disposed unsymmetrically and laterally of the longitudinal center-line of the base, so that the contact 1% is in position to cooperatev with the contact 30.

When the-parts are to be assembled, the spring tensioning element 53 (Fig. 5) is arranged with its web portion 59 resting directly upon the top surface 25 of the bushing 24 (assuming that the bushing is used) to which it is clamped or anchored by the head 8d of the screw 83. The hook 53 of the spring tensioning element 53 is engaged over the fulcrum edge 84? of the spring 71?, and the spring '71 isthen bowed downwardly until its edge 73 can be snapped into the V-notch ll) of the part 102. Inthis double-action switch, the bracket 33 (Fig. ll) is used. This bracket 33 has a threaded opening at its free end for the reception of a vertical stop screw 35 having a rounded tip in (Fig. l2) of insulating material which, in the normal or non-actuated position of the parts, contacts the concave upper surface of the spring 71 In this double-action switcn the base is provided with a vertical bore which receives a second adjustablestop screw 112, coaxial with the screw 35 and 5 below. the-spring-71, the locations of the opposedends' of screws 35 and- 112 determining the pressure between thecontact button 109 and the respective fixed, contacts 87 and 30. To retain the screw 35 in adjusted position, a resilient arm 113, below the bracket 33, has a screw threaded aperture for the reception of the screw 35, the arm 113 being so bent that it exerts axial pressure against the screw, thus tending to bind the latter and prevent its accidental rotation. Any suitable means may be provided for holding the stop screw 102 in adjusted position.

Referring to diagrammatic Fig. 15, the line W represents the tension element of a single-action snap switch embodying some but not all of the principles of the present invention, this tension element being anchored at one end at the point. H and its opposite end being hingedly connected at the point N to one end of a compression spring whose line of action is shown at C, and whose opposite end has pivotal engagement with the fixed abutment 49, the pivotal axis being in a horizontal plane L which is below the anchorage H, and midway between the vertically spaced stops TS and BS. The spring is always under some compressive stress. As shown, there is a movable contact K at the hinge connection point N between the parts W and C, and this contact normally engages the fixed stop TS, the compression spring holding the contact K with substantial pressure against the stop TS. The contact K may, at times, move from engagement with the stop TS to the bottom stop BS.

The switch is operated by means of an actuator applying force, in the direction of the arrow Z at a point A which is intermediate the ends of the tension member W. Since the tension member is inextensible, although very flexible, this application of force bends it so that it then comprises two straight portions (to the left and right r..- spectively of the point A) which intersect atan obtuse angle at the point A where the element W is bent. Since the over-all length of the tension member W remains constant, the connection point N (between the parts W and C) Slides horizontally to the right along the face of the top stop TS, which results in a shift in the line of action of the compression spring C and also in the further stressing of the spring, resulting in an increase in the component of force which presses the contact K against the stop TS. As the actuator is further depressed, the horizontal sliding movement of the point N with accompanying increase of compression of the spring continues until a position of the parts is reached wherein the tension member is so deformed that that portion J of the tension element, directly to the left of the point A of application of force, is aligned with the spring member C. This is the first critical or dead center position of the switch movement. Any subsequent differential movement of the actuator below the point A moves the left-hand portion I of the tension element, that is to say the part to the left of the point where the element W is bent by the application of actuating force, so that it lies below the line of action of the spring C. The spring now exerts an unopposed component of force such that the portion J of the tension element (to the left-of the point where element W is bent) swings about that point as a center. Since the spring pivots about its contact with the abutment 49 while the tension member pivots about the point of application of actuating force, the result is that the spring expands and supplies energy such as to carry the point N down to the point N where the contact K engages the bottom stop BS, this movment of the contact K from the stop TS to the stop BS being a sudden snap action.

Upon release of the actuating force the contact K moves back again from the stop BS to the stop TS with a similar snap action. This is by reason of the fact that the point H, about which the tension member (as a whole) pivots is spaced above the horizontal line L which passes through the pivotal axis of the spring C at the abutment 49 and which lies midway between the top and bottom stops TS and BS. Thus, as the actuating force is gradually removed from the't'ension element W (it being assumed that the point where the element W is bent is slightly below the point A in Fig. 15) the tension element W begins to straighten out, thus increasing in effective length so that the spring causes the common point of connection N to move to the left along the stop BS This results in a decrease in the spring force available to press the contact K against the bottom stop. As the spring is constantly tending to elongate the tension element W, the latter eventually reaches a position such that that section I of the tension element to the left of the flexure point at M, where it is bent by application of actuating force, is in alignment with the line. of action of the spring C. However, at this time the the tensioning element is still partially deflected, there still being an obtuse angle between the section I of the tensioning element and that rigid section which is to the right of the point of flexure at M. Assuming that the pressure at the actuating point continues to diminish and since the tensioning element W isnow free to pivot about the. point H (which is above the pivotal point of the spring at the abutment 49) there results a component of force acting upwardly which suddenly snaps the contact K upwardly to its initial position in contact with the top stop TS.

Figs. 16 to 18 diagrammatically illustrate the operation of an actual single action switch of the present invention. The part 53 in these views is a very flexible but substantially inextensible element, anchored at one end at the point 84 and hingedly connected at its opposite end, at the point N, with the compression spring 71.. The opposite end of this compression spring has pivotal contact with the normally fixed abutment 49 at the end of part 45 (Fig. 7), the pivotal axis being in the horizontal line L passing through the anchorage at 84 and midway be-' tween top and bottom stops TS and BS respectively. The tension element 53 extends upwardly from the anchorage at 84 and over the fixed hump or fulcrum member 40, and in the initial position of the parts, as shown in Fig. 16, holds the contact button K, which is secured to the spring member 71 at the point N, with substantial pressure against the stop member TS. In this position those portions of the tension element which extend from the flexing pointM to the point N and from the flexing point at M to the fulcrum point, respectively,-are straight and in alignment. It is important that the point of tangency of the part 53 with the hump 40 be above the line L. Actuating force is applied at the point A to that part of the tension member 53 which is stiffened by the vertical flange 70. This force, acting downwardly, swings the stiffened part of the tension element down about its righthand end which rests upon the hump 40 as an axis, to the position shown in Fig. 17 in which position that section I of the tension element, extending from the left-hand end M of the stiffening flange to the point N, is aligned with the line of action of the compression spring 71. This is the first neutral or dead center position and, if the actuating force be continued, so as to move the point of application from the position A of Fig. 17 to some position very slightly below it, the contact button K suddenly snaps down from the position of Fig. 17 to that of Fig. 18 where it engages the lower stop BS. The section I of the tension element is still substantially straight but intersects the flanged portion of the tension element at the point M at an angle whose apex is in a horizontal plane below that of the fixed end of the tension element atthe point 84. Upon release of the actuating force, the contact K snaps back to engage the top stop TS, for the reasons'described with reference to the switch of Fig. 15.

This is by reason of the fact that the fulcrum point about which all of the tension element (to the left of the fulcrum point) pivots, is spaced above the horizontal line L which passes through the pivotal axis of the spring C at the abutment 49. Thus as the actuating force is area-"71s gradually released from the tension element (it being assumed that the point where the tension element bends transversely is slightly below the point A the tension element begins to straighten out, allowing the spring to elongate, until that part I of the tension element to the left of the point M is aligned with the spring. However at this time the tension element is still partially deflected, there still being an obtuse angle between the part I of the tension element and the stiffened portion 70 of the tension element. As the actuating force continues to diminish (and since the tension element is free to pivot at the point where it contacts the fulcrum 40, which is above the horizontal plane L of the abutment 49), there results a component of force acting upwardly which swings the spring about the abutment 49 until the spring and the portion J of the tension element are aligned, whereupon the spring expands and suddenly snaps the contact K upwardly to its initial position in contact with the stop TS.

In Fig. 18 the character A represents the final position of the point of application of actuating force, corresponding to that indicated by the character A in Fig. 15. Thus the distance A--A in Fig. 18 represents substantially the maximum distance through which the point of application of force travels.

Comparing Figs. 15 and 18, it will be noted that in the switch of the present invention, a substantially less movement (A-A of the actuator is required to snap the switch than is necessary in aswitch constructed as suggested in Fig. 15. It may further be noted that the point of application A,- as shown in Fig. 16, might be moved much nearer to the hump 40 than shown in Figs. 16, 17 and 18, and since the stiffened part of the tension member 53 acts as a lever (turning about the point of tangency of the tension member with the hump 40) it is possible to decrease thenecessary motion of the actuator for operating the switch to a. very small amount, for instance to a distance of the order of 0.001 inch. Thus when sufiicient force is available for actuating the switch, the actuator may be arranged so that it need move through but a slight distance in snapping the switch. On the other hand, if the available actuating force is a lesser amount, the point of application may be moved to the left, as compared with the position shown in Fig. 16. A similar result can obviously be obtained by shifting the hump 40 whileleaving the line of action of the actuating force unchanged.

Referring to Figs. 21 and 22 which diagrammatically illustrate the principle of operation of a double action switch such as that shown in Fig. 12, the letter P designates the horizontal plane of the surface to which the right-hand end portion of the non-rigid spring tensioning element W is anchored by the screw 84. This plane H lies midway between vertically spaced stop elements 35 and112 which, so far as their movement-limiting function is concerned, correspond to the parts 35 and 112 of Fig. 12.

The spring tensioning element W extends upwardly from its anchorage 84 and over the'fixed arcuate deflector or fulcrum member 40, leaving the latter at the point of tangency U (which defines a pivotal axis about which the major portion of the tensioning element may swing) and being joined at its opposite end by a hinge connection or the equivalent to the left-hand end of the compression spring whose normal line of action is indicated by the-line 71 The'hingeaxis, where the spring and tensionnig element are joined, is indicated at N. The springis held under a certain normal degree of compression by the inextensible element W, it being understood that its right-hand end, as here illustrated, the

spring, engages a normally fixed abutment.

The secondaryv movement of the switch comprises a rigid arm diagrammatically indicated merely by lines 106, 107, 108 (corresponding in function to the part 1020f- Eig.12),.comprisingthe106 which is'fulc'rumed at 64'near-"the anchorage of the tensioning" element W and in a plane corresponding to the plane of the line L of Fig. 16. This rigid arm also comprises the upright portion 107, there being a notch at the junction of the parts 106 and 107 which defines a pivotal axis for the right-hand end of the spring, the part 1496 thus forming a rigid but movable abutment for the spring. The arm also has the portion 108 which carries the contact button 109 movable between the fixed contacts 87 and 30. the spring stress normally holding the contact button 109 in engagement with the bottom contact 30. Upward motion of the hinge joint at N is limited by the stop 35*.

In operating the switch, the actuator applies downward force to the non-stretchable tensioning element W at the point A. That portion of the tensioning element W which lies to the left of the fulcrum point U is designated by the characters W and W' respectively, the line of action of the actuating force being at the junction of these parts. (As here illustrated for simplicity in description but without limiting intent, the actuating force is applied to the extreme end of the lever portion W of the element W, so that no multiplication of the motion is obtained.) The part W is stiffened so that it acts as a lever pivoting about the fulcrum U. Since the element W (except for its stiffened portion) is freely bendable, the force applied at A- deflects the element W (as though it were hinged at the point A) so that it takes a shape such as indicated, for example, at W where the rectilinear parts W and W intersect at an obtuse angle at A As the actual linear length of the part W remains constant, such deflection causes the hinge point N to move horizontally to the right, further compressing the spring.

When, by the deflection of part W, the point of application of actuating force reaches the position A the part W of the tensioning element is in the line of action 71' of the spring. This point is the first dead center position of the primary movement. Slight further downward motion of the point of application of actuating force, below the point A causes the spring to exert an unopposed, downward component of force so that the part W of the tensioning element pivots about the lowest or final location of the point of application of actuating force, and the spring pivots about the abutment point 110. By reason of the difference in lengths and locations of the centers of rotation of the part W and the spring, the spring slightly expands, providing energy which sufiices to continue the movement of the parts until the hinge point N engages the stop 112 the parts thus completing their motion with trip-free action.

As the line 71 of the action of the spring force passes a line joining the points 64 and 110 (this position constituting the first dead center position of the secondary movement) the torque exerted by the spring is reversed with the result that the spring swings the member 106 about its fulcrum at 64 to the position indicated by the broken line 106 (Fig; 21) with the contact 109 firmly engaged with the contact 87.

The parts are restored to normal position by the spring when the actuator is released. As the pressure of the actuator is gradually removed from the tensioning element W the lattertends tobecome more nearly straight. Thus thepoint of application of actuating force may be considered to move upwardly from its final position A to a po'sitionA (Fig. 22-), at which the line of action of the spring coincides with the part W of the tensioning element W. However, it is important to note that at this instant, the parts WP and' W still make a slight angle with each other. This is the second dead center position of the primary movement.

As the actuating force continues to be released, and since the spring is still compressed, the tensioning element W eventually returns to its original position at which it is substantially rectilinear from the point N to thep'o'intU. The spring force being unopposed during this'la'tter motion causes'the'hinge point'N'to move up wardly into engagement with the stop 35 During this time the spring is expanding, furnishing energy to complete the movement of the parts with trip-free motion. At the second dead center position of the secondary movement, where the line of action of the spring passes through the points 110 and 64, the torque exerted by the spring on the part 106 is again reversed whereby the part 100 is snapped down to bring the contact button 109 into engagement with the lower contact 35.

In the present switch it is possible to use a tension element longer than those customarily employed in prior switches of this type and of standard dimensions, and to anchor it at the usual point in a switch of standard dimensions, but since the arms 54 and 55 of the tension element, at points adjacent to the righthand ends of the rigid or lever portions of the arms, rest upon the upwardly convex surfaces of the fulcrum members 40 and 41, the tension element being under tension where it overlies the fulcrum members, the application of actuating force to the rigid or lever portions of the arms 54 and 55 bends said arms transversely at their points of contact with the rigid fulcrum members and thus the. tension element cannot sag or assume a reverse curvature between its anchored end and the point of application of force. Thus the full motion of the force applying element is usefully employed, as contrasted with usual prior arrangements wherein a substantial portion of the work expended in operating the switch is consumed in bending the tension element to a reverse and useless curvature. Manifestly the base may be so designed as to shift the position of the hump in one direction or the other in accordance with the particular condition for which the switch is designed, and the height of the hump may likewise be varied. V

By adjustment of the stop screws 35 and 112 the pressure between the button 109 and the bottom and top contacts respectively may be varied at will, it being noted that in the normal position of the parts, as'shown in Fig. 12, any downward motion of the screw 35 will decrease the effective spring force tending to hold the button 109 down against the contact 30. On the other hand, upward motion of the screw 112 has the effect of decreasing the pressure between the button 109 and the top contact after the spring has been snapped.

While the simple form of spring-abutment illustrated in Fig. 7 is desirable, it is contemplated that the abutment may be of other shapes, and with provision for greater amount of adjustment of its spring contacting end, if desired. For example, as illustrated in Fig. 24, the part 45", which has the notch in its end to provide the fulcrum for the spring 72, is formed as one end portion of a strip of stiffly resilient metal which is doubled at 100 to provide the lower ply 45 and which has an opening at is twoply portion for the reception of the screw 31 which anchors the tension element 53. The lower ply 45 of this strip of metal has a downwardly directed leg 45 which is fitted into a socket in the base 20. By turning the screw 81 the part 45 may be flexed up or down so as to vary the position of the end of the spring 72.

A slight variation in the carrier for the upper contact is shown at 87 in Fig. 19.

Figs. 25, 26 and 27 illustrate a modified form of actuator and spring tensioning element. In this arrangement the spring tensioning element 53 (Fig. 26), which is anchored at its right-hand end (not shown) by a screw such as illustrated in Figs. 2 and 12, for example, and which passes over the hump or deflector elements 40 and 41, has its stiffening flanges 69 and 70 turned upwardly instead of downwardly. At the proper point in the length of these flanges, that is to say at the place at which the actuating force is to be applied, the flanges are provided with aligned circular openings which receive trunnion elements 92 and 92* which project from the opposite ends of the yoke member 89 of the actuator. The actuator comprisesthe button 88* which projects up through an opening in the cover 22. As here illustrated, the button is of polygonal, transverse section, for example square, as shown in Fig. 25, and passes loosely through an opening in the cover of a similar shape. The axes of the openings in the upturned flanges 69 and '70 are so located that the trunnions 92 and 92 rest upon the horizontal portions of the spaced legs 54 and 55 of the spring tensioning element. Since the force applied by the actuator acts upon the legs of the tensioning element at points closely adjacent to the stiffening flanges, the desired lever action, with multiplication of motion, is assured. This arrangement provides, in a very simple way, for applying the actuator force without tendency of the parts to bind due to the fact that the force applied to the button 88 may not always be exactly vertical, and with assurance that the actuator cannot rotate so as to disengage the spaced legs of the tensioning element.

For convenience in description reference has been made to the right and left-hand ends of the switch base and of certain parts of the switch and the terms up and down, above and below have likewise been employed, but it is to be understood that these terms are only used with reference to the accompanying drawings and in particular with respect to- Figs. 1 to 5 inclusive, Fig. 7 and Figs. 11 to 19 inclusive, and are not to be considered as in any way limiting the position in which the switch may be used.

While one desirable embodiment of the invention has beenherein disclosed by way of example, it is to be understood that the basic principles herein disclosed may be applicable to switches of widely different types and that the invention is broadly inclusive of any and all modifications falling within the scope of the appended claims.

I claim:

1. A snap action switch having in combination a rigid elongate base provided at one end with a supporting surface and near its opposite end with vertically spaced normally fixed contacts, an elongate thin and flexible tension element, aportion of one end of the tension element resting upon said supporting surface and being clamped thereto, a compression spring, a normally immovable abutment for one end of the compression spring, and means for adjusting'the height of the abutment, the opposite end of the compression spring being hingedly connected to the tension element, an actuator for applying downward force to the tension element for flexing the latter transversely, rigid fulcrum means defining a transverse pivotal axis, above the level of the supporting surface about which the tension element may bend, said fulcrum means being carried by the base and having said pivotal axis spaced longitudinally of the base from the clamped portion of the tension element, and a movable contact engageable alternatively with one or the other of the fixed contacts and which moves down in response to the snap action of the compression spring, the compression spring normally holding the movable contact in engagement with the upper fixed contact.

2. A snap action switch according to claim 1, wherein an elongate portion of the normally flexible tension element, located between the place of engagement of the tension element with the fulcrum and the hinge connection of the tension element with the compression spring, is stiffened to constitute a lever arm.

3. A snap action switch according to claim 1, wherein the fulcrum member has an upwardly convex surface with which the tension element contacts, that portion of the tension element which extends from its fixed end toward said point of contact being free from engagement with other parts, the point of contact of the tension element with said convex surface defining the transverse pivotal axis about which the major portion of the tension element rocks in response to the application of actuating force.

4. A snap action electrical switch comprising an elongate, rigid base, opposed spaced fixed contactsat the lefthand end of the base, means providing a support adjacent to the right-hand end of the base, a tension element consis'ting of an elongate piece of thin and flexible sheet mater'ial of generally rectangular contour having a single large elongate unobstructed Central opening, thereby defining a pair of transversely narrow elongate, parallel arms connected at their ends by transverse web portions, the right-hand web portion having an opening, a screw passing through said opening for clamping said web against the aforesaid support, the base having at its opposite sides transversely narrow upstanding humps constituting fulcrum members which underlie the respective elongate arms of the tension element, said fulcrum members being spaced to the left from the clamping screw and those portions of the arms which extend from the clamped web to the points at which the arms make contact with the fulcrum members being free from contact with the base, a movable actuator which contacts said elongate arms of the tension element at points between said humps and the left-hand end of the tension element, a compression spring, hinge means connecting the lefthand end of the compression spring to the left-hand end of the tension element, a substantially rigid part providing an abutment for the right-hand end of the compression spring, a movable contact interposed between said fixed contacts, and means for transmitting motion from the compression spring to the movable contact.

5. A snap action switch comprising an elongate base having vertically spaced fixed contacts adjacent to one end, an elongate, flexible tension element having one end fixed to the other end of the base, a compression spring connected to the free end portion of the tension element, a movable contact interposed between the fixed contacts, and means for transmitting motion from the connected ends of the tension element and spring to the movable contact, the fixed and movable contacts being located to one side ofthe longitudinal center line of the base, the major portion of the tension element, intermediate its ends, consisting of two spaced parallel arms, and a rigid actuator for applying force simultaneously to said arms, said actuator comprising transversely spaced parts for contact with the respective arms, the tension elements and said actuator parts being so constructed and arranged that unequal effective force is applied to the two arms by the actuator.

6. A snap action switch comprising an elongate rigid base having transversely spaced rigid humps which rise above the upper surface of the base proper and are located, one at each side respectively, of the base, and adjacent to but spaced from the right-hand end of the base, vertically spaced fixed contacts adjacent to the left-hand end of the base, an elongate, unitary, flexible but substantially inextensible tension element comprising spaced parallel arms united at their opposite ends respectively by webs, means securing the right-hand web to the base at a point to the right of said humps, the arms of the tension element extending toward the left-hand end of the base and overlying and contacting the respective humps, a compression spring, a normally immovable member extending longitudinally of the base and Whose right-hand end portion is disposed between said humps and which provides an abutment for the right-hand end of the compression spring, means providing a hinge joint between the left-hand end of the compression spring and the left hand web of the tension element, the spring keeping the tension element under longitudinal tension, means stiffening that portion of the length of the tension element which extends from its contact with the humps to a point just to the right of the abument, a movable contact interposed between said fixed contacts, means for transmitting motion of the spring to the movable contact, and means for applying actuating force simultaneously to the two arms of the tension element at points to the left of the respective humps, thereby downwardly to'flex the tension element, just tothe left of its stiffened portion, until the i6 point of flexure passes below the point at which the spring contacts the abutment to cause snap action of the spring.

7. snap action switch according to claim 6, wherein each arm of the tension element is provided with a stiffening flange disposed substantially at right angles to the arm proper, said flanges being arranged closely adjacent to the inner surfaces of the respective humps, the right-hand ends of said flanges being located to the left of the highest points of the humps, and the left-hand ends of the flanges being located to the right of the abutment for the compression spring.

8. A snap action switch according to claim 6, wherein the right-hand ends of the humps rise relatively abruptly from the upper surface of the base proper, while at their left-hand ends the humps slope gradually down toward the upper surface of the base proper.

9. A snap action switch comprising an elongate rigid base having a substantially horizontal upper surface and having vertically spaced fixed contacts adjacent to its lefthand end, an elongate, unitary, flexible but substantially inextensible tension element extending lengthwise of the base, means fixing the right-hand end portion of the tension element to the base near the right-hand end of the latter, fulcrum means for the tension element, the fulcrum means being elevated above the upper surface of the base proper, said fulcrum means being spaced from and to the left of the fixed end of the tension element, the tension element overlying said fulcrum means, a compression spring, a normally immovable member on the base which provides an abutment for the right-hand end of the compression spring, means operative to bend said normally immovable member thereby to vary the height of the abutment, means providing a hinge joint between the left-hand end of the tension element and the left-hand end of the spring, a movable contact interposed between the fixed contacts, means for transmitting motion of the compression spring to the movable contact, the parts being so constructed and arranged that the movable contact normally presses against the upper fixed contact, means for applying a downwardly directed actuating force to the tension element at a point at the left of said fulcrum means and to' the right of the location of the spring abutment, the elevated fulcrum means constituting a bridge over which the tension element is held taut by the compression spring, that portion of the tension element which extends from its contact with the fulcrum means to its hinge connection to the compression spring'normally being under substantially pure tension stress.

10. A snap action switch according toclaim 9, wherein the vertically spaced fixed contacts and the movable contact are located to one side of the longitudinal center line of the base, the tension element and compression spring being so stressed as normally to keep the movable contact in engagement with the upper fixed contact whereby there is developed a tendency to twist the tension element so that one marginal portion of the tension element would normally be more elevated than the other, and means for neutralizing the effects of such tendency of the tension element to twist in response to the application of actuating force.

11. A snap action switch having in combination a rigid elongate base provided near its right-hand end with a supporting surface and near its left-hand end with vertically spaced normally fixed contacts, an elongate, thin but substantially inextensible tension element of a material having a degree of flexibility comparable to that of berylium-bronze of a thickness of the order of 0.006, a portion of the right-hand end of the tension element resting upon said supporting surface, means for clamping said end of the tension element to the base, a compression spring of a material stiffer than that forming the tension v element, a substantially rigid part providing an abutment for the right-hand end of the compression spring, means providing a hinge joint between the left-hand end of the compression spring and the left-hand end of the tension element, rigid fulcrum means for the tension element about which the latter bends transversely in response to the application of downwardly directed actuating force, the contact of the tension element with the fulcrum means being at an elevation above the upper surface of the base proper and being spaced longitudinally of the base from the clamped end portion of the tension element and between said clamped end portion and the actuator, the upper face of that part of the tension element which extends from its clamped portion to the place where it engages the fulcrum means being normally substantially flat, an actuator for applying downwardly directed actuating force to the tension element at a point intermediate said abutment and the fixed right-hand end of the tension element thereby to flex the latter downwardly, and a movable contact which normally engages the upper fixed contact and which is moved down to engage the lower fixed contact by the snap action of the compression spring when downward actuating force is applied to the tensioning element.

12. In combination in a snap action switch of the kind wherein an elongate rigid base supports vertically spaced contacts adjacent to its left-hand end and an elongate tension element of thin but flexible and substantially inextensible material extends longitudinally of the base and has its right-hand end fixed to the base, a compression spring, means hingedly connecting the left-hand end of the compression spring to the left-hand end of the tension element, a substantially rigid member carried by the base and which provides an abutment for the right-hand end of the compression spring, the tension element having an elongate portion which is stilfened to constitute a lever, the right-hand end of the stiffened portion being spaced from the fixed right-hand end of the tension element, said stitfened portion terminating to the right of the spring abutment, n'gid fulcrum means to the left of the fixed right-hand end portion of the tension element and spaced from the latter, said fulcrum means providing a bridge, elevated above the level of the fixed end of the tension element, over which the tension element is held taut by the compression spring, means arranged to the left of the fulcrum means for applying downwardly directed actuating force to the stilfened portion of the tension element thereby to swing said stilfened portion as a lever in a counterclockwise direction, the left-hand end of the stiffened portion of the tension element defining a definite point of transverse flexure in the length of the tensioning element, said point of flexure moving downwardly below the level of the spring abutment in response to the application of downwardly directed actuating force thereby causing the compression spring to snap, a movable contact interposed between the fixed contacts, and means for transmitting snap motion of the compression spring to the movable contact, that portion of the length of the tension element which extends from the fulcrum means to its hinge connection to the compression spring being normally substantially straight.

13. A snap action switch comprising an elongate rigid base of insulating material, a normally fixed abutment intermediate the ends of the base, two vertically spaced, fixed, electrical contacts adjacent to one end of the base, a movable contact interposed between said fixed contacts and normally engaging the upper of said contacts, a resilient compression element having one end engaging the abutment and having its opposite end adjacent to but spaced from the fixed contacts, an elongate, flexible, tension element having one end movably joined to the lastnamed end of the compression element and which normally overlies the compression element and bridges the point of engagement of the compression element with the abutment, the opposite end of the tension element being adjacent to that end of the base which is remote from the fixed contacts, means anchoring said latter and of the tension element to the base, means for transmitting motion of the joined ends of the compression and tension elements to the movable contact, rigid fulcrum means mounted on the base and underlying the tension element adjacent to but spaced from the anchored end of the latter, means stifl'ening a portion of the tension element which extends from adjacent to said fulcrum means to adjacent to the abutment, and means for applying downwardly acting force to said stiffened portion of the tension element whereby the latter is caused to swing as a lever about the fulcrum means, and the unstiffened portion of the tension element, adjacent to the abutment, is downwardly flexed to pass below the point at which the compression element engages the abutment.

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